The invention relates to a method for triggering a plurality of valves and to a control block having a plurality of valves, in particular for mobile driven machines. From German Patent Disclosure DE 10 2004 048 706, it is known to trigger a magnet valve using a pulse width modulated (PWM) control signal.
To prevent the armature of the magnet valve from seizing in a particular position because of static friction, the control signal is acted upon by a low-frequency, so-called dither signal. This signal changes the duty factor of the control signal, so that seizing of the armature is prevented.
DE 10 2004 048 706 describes the problem of an unwanted fluctuation in the magnetic current, which can even damage the hydraulic system. For this reason, the PWM control signal and the dither signal are generated independently of a main control loop.
In mobile driven machines, for example, a plurality of hydraulic valves are often combined into control blocks. It has then been found that low-frequency fluctuations occur, with a frequency typically in the sub-Hertz range, for example from approximately 0.1 Hz to 0.001 Hz. These fluctuations cannot be regulated at all, or only with great difficulty, and lead to unwanted oscillations in the triggered consumer.
Tolerance-caused differences in frequency in the oscillating quartzes of the various valve electronics units are suspected to be the cause of the fluctuations.